This invention relates generally to means for aligning and mounting a removable member on a supporting member and more particularly to means suitable for aligning and mounting a printed circuit board (PCB).
In some applications it is important that a removable printed circuit board be mounted in precise alignment with a datum line on a supporting structure. For example, in replacing a printed circuit board having an optical element, the board must be aligned with the precision required for the optical element to operate in the system.
An important application for the present invention is in alignment of an amplifier printed circuit board bearing photodiodes for an opto-electronic transducer used in determining position and/or velocity of one member with respect to another member, such as where a reticle is affixed to a stationary frame and a transmission grating is affixed to a carriage for a read/write head in a magnetic disk data storage system. Typically, the disk recording medium is rotated at a constant speed and the head is flown over the surface of the disk on a gas film bearing and positioned to the appropriate track by the use of a linear voice-coil type of motor. The motor attached to the head carriage is controlled in respect to both velocity and position. As the carriage moves the head to the correct track address, it is brought to a controlled stop and positioned over the track by a stable servo loop.
An opto-electronic transducer will permit proper positioning of a magnetic read/write head on a disk usually having as many as 200 tracks per inch due to the extreme accuracy with which a scale and reticle can be produced using photographic techniques, provided the electronic circuits employed to detect motion of the scale relative to the reticle are adapted to operate with a proper degree of accuracy. This requires the elements-scale, reticle and photodiodes-to be properly aligned.
Alignment of the reticle with the photodiodes can easily be made with the necessary precision during factory assembly of an amplifier circuit board bearing the photodiodes and a frame bearing the reticle. The problem lies in effectively replacing the printed circuit board in the field with a minimum of effort and tools, but with the same precision as in the factory.
A typical opto-electronic transducer which may use the present invention to advantage is disclosed in a copending application Ser. No. 699,248 filed June 24, 1976. Others are disclosed in U.S. Pat. Nos. 3,783,277 and 3,809,895. However, the present invention is not to be construed as being limited to printed circuit boards carrying opto-electronic transducers since it may be used to equal advantage in any assembly which requires alignment of a removable member such as a printed circuit board.